1. Field of the Invention
The present invention relates to polyhydroxyalkanoate (PHA) containing novel a constitutent unit and a producing method therefor. More specifically, it relates to a method for producing biodegradable novel PHA containing a 3-hydroxy alkanoic acid unit having 2-thienylsulfinyl radical and 2-thienylsulfonyl radical as substituents at the end of the side chain by culturing a microorganism having the PHA producing ability thereby producing and accumulating therein PHA containing 3-hydroxy alkanoic acid unit having corresponding 2-thienylsulfonyl radical as the substituent, and selectively oxidizing sulfur of sulfide type in such PHA thereby converting it into sulfonyl radical and sulfinyl radical.
The present invention also relates to a charge control agent, a toner binder and an electrostatic latent image developing toner to be used in a recording method utilizing an electrophotographic method, an electrostatic recording method, a magnetic recording method etc., and an image forming method and an image forming apparatus utilizing such toner. In particular, it relates to a charge control agent, a toner binder, an electrostatic latent image developing toner, an image forming method and an image forming apparatus to be employed in electrophotography, electrostatic recording, electrostatic printing such as a copying apparatus, a printer or a facsimile in which an image is formed by forming in advance a toner image on an electrostatic latent image bearing member (hereinafter simply called image bearing member) and then transferring such toner image onto a transfer material. More specifically, it relates to a negatively chargeable charge control agent, a toner binder and an electrostatic latent image developing toner utilizing the same, and an image forming method and an image forming apparatus utilizing such toner.
2. Description of the Related Art
It has already been reported that various microorganisms produce poly-3-hydroxybutyric acid (PHB) or other PHA's and accumulate such products therein (“Biodegradable Plastics Handbook”, edited by Biodegradable Plastics Association, N.T.S.Co., p. 178-197 (1995)). Such PHA produced by the microorganisms can be utilized for producing various products for example by fusion, like the conventional plastics. Also the PHA produced by microorganisms, being biodegradable, has the advantage that it can be completely decomposed by the microorganisms in a nature, and, unlike the various conventional synthesized polymers, is free from contamination resulting from remaining in the natural environment. It also shows satisfactory matching with the living tissues and is expected in the applications as the soft material for medical use.
Such microorganism-produced PHA is known to assume various compositions or structures depending on the kind of microorganism, composition of culture medium and culture condition employed for production, and researches have been made for controlling such composition and structure, principally for improving the physical properties of PHA.    [1] At first, for the biosynthesis of PHA by polymerizing a monomer unit of relatively simple structure such as 3-hydroxybutyric acid (hereinafter abbreviated as 3HB), following references are known:            (a) PHA containing 3HB and 3-hydroxyvaleric acid (hereinafter abbreviated as 3HV) as monomer units:                    Japanese Patent Publications Nos. 6-15604, 7-14352 and 8-19227, and Japanese Patent Application Laid-open No. 5-7492;                        (b) PHA containing 3HB and 3-hydroxyhexanoic acid (hereinafter abbreviated as 3HHx) as monomer units:                    Japanese Patent Applications Laid-open Nos. 5-93049 and 7-265065;                        (c) PHA containing 3HB and 4-hydroxybutyric acid (hereinafter abbreviated as 4HB) as monomer units:                    Japanese Patent Application Laid-open No. 9-191893;                        (d) PHA containing 3-hydroxyalkanoate of 6 to 12 carbon atoms as monomer unit:                    Japanese Patent No. 2642937; and                        (e) biosynthesis of PHA utilizing a single fatty acid as the carbon source, providing PHA substantially same as (d):                    Appl. Environ. Microbiol., 58(2), 746(1992).                        
All these references report production of PHA consisting of a monomer unit having an alkyl radical in the side chain, namely “usual PHA”, synthesized by β-oxidation of hydrocarbon or the like by microorganisms or by fatty acid synthesis from saccharide.    [2] However, for wider application of microorganism-produced PHA, for example for application as functional polymer, PHA having a substituent other than alkyl radical in the side chain, namely “unusual PHA”, is anticipated to be extremely useful. Examples of hopeful substituent for this purpose include a radical containing an aromatic ring (phenyl radical, phenoxy radical, benzoyl radical etc.), an unsaturated hydrocarbon radical, an ester radical, an allyl radical, a cyano radical, a halogenated hydrocarbon radical and an epoxide present on the side chain. Among these, PHA having an aromatic ring on the side chain is actively investigated. For biosynthesis of PHA having an aromatic ring on the side chain, there are known following references:            (a) PHA containing phenyl radical or a partially substituted radical thereof (substituted phenyl radical etc.):                    Makromol. Chem. 191, 1957-1965(1990) and Macromolecules, 24, 5256-5260(1991) report that Pseudomonas oleovorans produces PHA containing 3-hydroxy-5-phenylvaleric acid as a unit, from 5-phenylvaleric acid as substrate.            Also Macromolecules, 29, 1762-1766(1996) reports that Pseudomonas oleovorans produces PHA containing 3-hydroxy-5-(p-tolyl) valeric acid as a unit, from 5-(p-tolyl) valeric acid as substrate.            Also Macromolecules, 32, 2889-2895(1999) reports that Pseudomonas oleovorans produces PHA containing 3-hydroxy-5-(2,4-dinitrophenyl) valeric acid and 3-hydroxy-5-(p-nitrophenyl) valeric acid as units, from 5-(2,4-dinitrophenyl) valeric acid as substrate.                        (b) PHA containing phenoxy radical or partially substituted radical thereof (such as substituted phenoxy radical):                    Macromol. Chem. Phys., 195, 1665-1672(1994) reports that Pseudomonas oleovorans produces a PHA copolymer containing 3-hydroxy-5-pnenoxyvaleric acid and 3-hydroxy-9-phenoxynonaic acid as the units, from 11-phenoxyundecanoic acid as substrate.            Also Japanese Patent No. 2989175 discloses inventions relating to homopolymer consisting of a 3-hydroxy-5-(monofluorophenoxy) pentanoate (3H5(MFP)P) unit or a 3-hydroxy-5-(difluorophenoxy) pentanoate (3H5(DFP)P) unit, copolymer containing at least a 3H5(MFP)P unit or a 3H5(DFP)P unit, a novel strain of Pseudomonas putida capable of producing these polymers, and a method for producing the aforementioned polymers utilizing Pseudomonas genus. This patent specification teaches, as the effects of such inventions, that PHA polymer having a phenoxy radical substituted with 1 or 2 fluorine atoms at the end of the side chain can be biosynthesized from a long-chain fatty acid having a substituent and that thus produced PHA has a high melting point and is capable of providing stereoregularity and water repellency while maintaining satisfactory working properties.            In addition to the partially substituted phenoxy radical having fluorine substituent on the ring, there are also investigated partially substituted radical having cyano or nitro radical on the ring.            Can. J. Microbiol., 41, 32-43(1995) and Polymer International, 39, 205-213(1996) report production of PHA containing 3-hydroxy-6-(p-cyanophenoxy) hexanoic acid or 3-hydroxy-6-(p-nitrophenoxy) hexanoic acid as the monomer unit by Pseudomonas oleovorans ATCC 29347 strain and Pseudomonas putida KT2442 stain, from octanoic acid and 6-(p-cyanophenoxy) hexanoic acid or 6-(p-nitrophenoxy) hexanoic acid as substrate.            These references relate to PHA having an aromatic ring on the side chain, instead of the usual PHA in which the side chain consists of an alkyl radical, and are effective in obtaining polymer of physical properties resulting from such aromatic ring.                            [3] Also as a new category not limited to changes in the physical properties, investigation is also made for producing PHA having an appropriate functional radical on the side chain, thereby obtaining PHA with new functions utilizing such substituent.
For example Macromolecules, 31, 1480-1486(1996) and Journal of Polymer Science: Part A: Polymer Chemistry, 36, 2381-2387(1998) etc. report a method of biosynthesizing PHA containing a unit having vinyl radical at the end of the side chain and then executing epoxylation with an oxidant, thereby obtaining PHA having a high reactive epoxy radical at the end of the side chain.
In addition to such vinyl radical, for biosynthesis of PHA containing a unit having sulfide type sulfur (—S—) for which high reactivity is anticipated, Macromolecules, 32, 8315-8318(1999) reports that Pseudomonas putida 27N01 strain produces PHA copolymer containing 3-hydroxy-5-(phenylsulfanyl) valeric acid and 3-hydroxy-7-(phenylsulfanyl) heptanoic acid as the units, from 11-(phenylsulfanyl) valeric acid as substrate.
On the other hand, the conventional electrophotography includes various methods so far proposed but in general consists of forming an electrical latent image by various means on an image bearing member (photosensitive member) utilizing a photoconductive substance, then developing such latent image with toner to obtain a visible image, transferring the toner image onto a transfer material such as paper if necessary, and fixing the toner image on the transfer material with heat and/or pressure thereby obtaining a copy. For rendering the electrical latent image visible, there are known cascade development method, magnetic brush development method, pressure development method etc. Also there is utilized a method of employing magnetic toner and a rotary developing sleeve having magnetic poles at the center, and causing the magnetic toner to fly from the developing sleeve to the photosensitive member.
For developing electrostatic latent image, there are known a two-component development method employing two-component developer consisting of toner and carrier, and a one-component development method employing one-component developer consisting solely of toner and not containing carrier.
The colored fine particles, generally called toner, are essentially composed of binder resin and a coloring material, and also contain magnetic powder etc. if necessary. For providing the toner with electric charge, there can be utilized charging characteristics of the binder resin itself without utilizing the charge control agent, but satisfactory image quality cannot be obtained because of insufficiency in stability of charge in time and in moisture resistance. Therefore, a charge control agent is added to the toner in order to retain and control the charge.
The charge control agents presently known in this technical field include, for example for negative triboelectricity, metal complexes of azo dyes, those of aromatic dicarboxylic acid, and those of salycilic acid derivatives. Also for positive charge control agents, there are known nigrosin dyes, triphenylmethane dyes, various quaternary ammonium salts and organic tin compounds such as tibutyltin oxide.
From the standpoint of environmental protection, it is recently desired worldwide to further reduce the wastes and the environmental pollution. Such requirements are same also in the electrophotography. In fact the discarded amount of the printed papers, waste toner after use and copy papers is increasing year after year with the popularization of the imaging apparatuses, and, from the standpoint of securing the global environment, it is strongly desired to further reduce the wastes and to use substances selected in consideration of the environment.
In order to meet such requirements, there are investigated charge control agents consisting of colorless compounds free from heavy metals or of polymers. Examples of such compounds include those disclosed in the U.S. Pat. Nos. 4,480,021, 4,442,189 and 4,925,765, and the Japanese Patent Applications Laid-open Nos. 60-108861, 61-3149, 63-38958 and 63-88564, but such compounds are not sufficient in the performances of the charge control agent, for example in the charge amount, start-up characteristics of charging, stability in time and environmental stability. In general the polymer charge control agent for providing the toner with the negative charging property is often composed of copolymer of styrene and/or α-methylstyrene and alkyl(meth)acrylate ester or alkyl(meth)acrylate amide having a sulfonic acid radical (Japanese Patent Applications Laid-open Nos. 7-72658 and 8-179564, and Japanese Patent Nos. 2114410, 2623684 and 2807795). Such materials are advantageous as they are colorless, but have to be added in a large amount in order to obtain the desired charge amount. Also the moisture resistance is anticipated to be insufficient since the sulfonic acid radical, serving as the anionic functional radical, apparently has hygroscopicity. Also there is anticipated insufficiency in the mutual solubility with the binding resin (binder) which is basically nonionic.
From the standpoint of environmental protection, developments are being made for biodegradable resin which can be decomposed in time by the function of microorganisms, and, as explained in the foregoing, there have been reported that various microorganisms produce and accumulate therein biodegradable resin having a polyester structure (PHA). Such PHA is known to assume various compositions or structures depending on the kind of microorganism, composition of culture medium and culture condition employed for production, and researches have been made for controlling such composition and structure, principally for improving the physical properties of PHA.
Also in the field of electrophotography, there has been proposed application of the biodegradable resin to the binder resin in the manufacture of toner. For example the U.S. Pat. No. 5,004,664 discloses toner containing biodegradable resin, in particular polyhydroxy butyric acid, polyhydroxy valeric acid, copolymer thereof or a blended substance thereof as a component. Also the Japanese Patent Application Laid-open No. 6-289644 discloses electrophotographic toner particularly for heat roller fixing, containing vegetable wax and biodegradable resin (for example microorganism-produced polyester, vegetable- or animal-derived natural polymer etc.), wherein the aforementioned vegetable wax is added to the binder resin in an amount of 5 to 50 mass %. Also the Japanese Patent Application Laid-open No. 7-120975 discloses electrophotographic toner containing butyric acid-based resin as the binder resin. Further, the Japanese Patent Application Laid-open No. 9-274335 discloses electrostatic latent image developing toner containing polyester resin, obtained by dehydration condensation-polymerization of a composition containing butyric acid and 3- or higher-functional oxycarboxylic acid, and a coloring agent. Also the Japanese Patent Application Laid-open No. 8-262796 discloses electrophotographic toner containing binder resin and a coloring agent, wherein the binder resin is composed of biodegradable resin (for example aliphatic polyester resin) and the coloring agent is composed of a water insoluble dyestaff. Also the Japanese Patent Application Laid-open No. 9-281746 discloses electrostatic image developing toner containing urethanized polyester resin, obtained by crosslinking polylactic acid with 3- or higher-functional polyvalent isocyanate, and a coloring agent. All these electrophotographic toners employ biodegradable resin as the binder resin, and are expected to be effective in contributing to securing the environment.
In any of the electrophotographic toners employing the aforementioned biodegradable resins as the binder resin, the charge control agent contains heavy metals such as chromium, cobalt, nickel, copper, zinc or iron. On the other hand, the use of biodegradable resin for the charge control agent has not been reported, and there is desired the material realizing further environmental protection.